This blog provides updated forecasts and comments on current weather or other topics

Saturday, January 15, 2011

Warm, Wet, and Windy

In education it is the three "R"s....Reading, wRiting, and aRithmatic. (ok, they might not have mastered spelling that well)

For the Northwest during flooding, mudslides, and pineapple express periods it is the three W's:Wet, Windy, and Warm.

SUNDAY UPDATE: I can't help myself....Richard Rogers of Vashon Island sent me this wonderful video demonstrating the tendency of the media (and yes even me) to describe active weather with lots of "W" s. Very funny....here is is:

After the very brief snow early in the week, we have switched into a period of extraordinary warmth and precipitation, with resulting flooding, slope failures, and production of Cascade concrete in the mountains.

Last night the temperatures only fell into the middle 40s and temps today got into the 50s, even under considerable cloudiness. Twenty degrees warmer than earlier this week.

The reason for this consistent moisture and warmth? We have had a strong jet stream passing to our north upon which low pressure centers passed northeastward roughly every 24-h. This pattern moves both warm air and moisture from the southwest...something known as an atmospheric river or in our case a pineapple express. Here is the latest infrared satellite photo:You can really see the stream of subtropical moisture.

And here is the predicted water vapor distribution at 4 PM. The purples shows the air with the highest water vapor content. Nice current of moist air moving our way.

Lets take a look at the predicted pressure and lower atmosphere temperature pattern at 4 PM (see first picture below) and the wind speeds aloft (near jet stream level) at roughly the same time (second image below). You can see that the jet stream is closely aligned with the moisture plume above (the moisture plume is roughly parallel to the jet stream but displaced a bit to the south). Looking at the sea level pressures, note the next Pacific disturbance, following the jet stream to the NE. See all those lines of constant pressure to the south of the low--that tells us there are strong winds.

As each of these lows have passed north of us the winds increass substantially over the region...like yesterday when winds hit 30-50 mph over western Washington.

This pattern is ideal for heavy rain over our region. Warm air can hold a great deal of water vapor. Strong winds push a lot of water vapor towards us and up our mountains where the vapor condenses into rain. Warmth means high freezing level, which helps flooding (falling snow doesn't run off).

Precipitation has been well above normal the past few months and these recent events are saturating the soils further...here is the precipitation at Sea-Tac for the past 12 weeks--we are a good 9 inches above normal and there has been a major uptick during the past few days. The weather service is warning of flooding on a number of local river systems (see map below) and we are starting to see increasing number of slope failures (e.g., mudslides). Red indicates predicted flooding. Yellow is bankfull.

There is an interesting angle about this regarding global warming. Most of our extreme precipitation events and serious flooding event are associated with atmospheric rivers like the above. Virtually all of these atmospheric rivers are connected with the jet stream (as shown above). Nearly all climate models indicate the jet stream will move north due to man-caused global warming. Does that mean the we will get less atmospheric rivers and LESS extreme precipitation as the jet moves north? That should be true for someone along the coast. This is why the simple arguments often provided by the media (global warming means more extreme precipitation and floods!!) may not be quite true for everyone. And here is an interesting tidbit...the number of extreme flooding events have DECLINED in northern CA and southern Oregon during the past fifty years. Is it already happening? Are we next for a dry out? My profession really has to get a better understanding of all this.

Cliff since this is your Blog please feel free to "suck" us into anything you choose. I trust your knowledge and balanced outlook. At 5:00 AM it is 48 here in Sequim and it rained heavy all night. Sometime in November I made the comment that the skiing would be very good in December to be followed by three major rain on snow events. This first one is a real doozy!

Off topic, but I was wondering if Cliff could comment on this short article on the NOAA plane: http://seattletimes.nwsource.com/html/localnews/2013930803_weatherplane13m.html. Do you think it will be a significant help, etc.? . . .

Cliff, thanks so much for all your comments and facts on weather. I got your book for Christmas and have been following your blog ever since. I've always loved our extreme weather and now you even make our gray rainy days sound exciting! When everyone at work was fussing over snow during the commute last week I kept saying it would happen later-now they will be following your blog too!Lori in Snohomish

Cliff, reading your blog titled Warm, Wet, Windy brought to mind an interview some years back when a meteorologist, perhaps yourself, used the phrase "Wetter, warmer, western Washington Winer weather".

This eventually led to a skit I wrote for Vashon's Church of Great Rain comedy show featuring only words beginning with W.Here is the skit for your amusement:http://tinyurl.com/4kz9lss

Hey BCG, I appreciate when Cliff is discussing the impacts of global warming on Pacific Northwest weather in a scientific and factual way. I am glad he isn't sucked into "AGW" denialist hype... Too many other websites and media have been.

With all due respect to Professor Mass whom I sincerely admire - have read/own his wonderful book and have attended several interesting lectures - it's not global warming/climate change that's in dispute, it's what portion of it is truly 'man made' (ie due to our production of CO2). I appoligize if I ruffled any feathers, but to my knowledge 'man made global warming' is a theory based largely upon computer models, and not a fact. http://thegwpf.org/opinion-pros-a-cons/2229-richard-lindzen-a-case-against-precipitous-climate-action.html

Can you provide a semi-technical description of "Column-integrated Water Vapor", as shown in one of your graphics today? Is the integration performed over a particular altitude (or pressure level) range? Thanks.